tpm2_commit(1)

📦
version 5.8 · 10 versions
, in arch rolling

💅 NAME

hey bestie, this is tpm2_commit(1) from the General Commands Manual, and it performs the first part of an ECC anonymous signing operation 💖 no cap, that's the whole NAME section and it ate.

🎀 SYNOPSIS

tpm2_commit [OPTIONS]

💖 DESCRIPTION

tpm2_commit(1) performs the first part of an ECC anonymous signing operation. The TPM will perform the point multiplications on the provided points and return intermediate signing values. The signing key is an ECC key. The key cannot be a sign+decrypt key and must have an anonymous signing scheme. TPM_ALG_ECDAA is the only supported anonymous scheme, periodt.

The signing key is lowkey the main character here: it's an ECC key, and it has rules. The key cannot be a sign+decrypt key and must have an anonymous signing scheme. TPM_ALG_ECDAA is the only supported anonymous scheme. Yes bestie, that's important, so I said it twice in spirit and kept every detail 🫶

🦋 OPTIONS

  • ARGUMENT=FILE — specify the input data used to derive the x coordinate of the basepoint ✨
  • --basepoint-y=FILE — specify the y coordinate of the basepoint 💫
  • --eccpoint-P=FILE — specify a point on the curve used by sign handle 🌸
  • --eccpoint-K=FILE — output ECC point K ≔ [ds](x2, y2) 🔥
  • --eccpoint-L=FILE — output ECC point L ≔ [r](x2, y2) 🔥
  • -u, --public=FILE — output ECC point E ≔ [r]P1 ✨
  • -t, --counter=FILE — specify file path to save the least-significant 16 bits of commit count 🎀
  • -p, --auth=AUTH — the authorization value for the created object 🔐
  • -c, --context=FILE — context object pointing to the the key used for signing. Either a file or a handle number. See section “Context Object Format” 👑
  • --cphash=FILE — file path to record the hash of the command parameters. This is commonly termed as cpHash.
NOTE: When this option is selected, The tool will not actually execute the command, it simply returns a cpHash. literally not me reminding you that this is the "just give me the hash" mode 💀

🦋 References

okay bestie, this is the reference zone — the algorithm specifier lore starts right below and it's giving encyclopedia but make it cute ✨

🔥 Algorithm Specifiers

Options that take algorithms support “nice-names”.

There are two major algorithm specification string classes, simple and complex. Only certain algorithms will be accepted by the TPM, based on usage and conditions.

🧚 Simple specifiers

These are strings with no additional specification data. When creating objects, non-specified portions of an object are assumed to defaults. You can find the list of known “Simple Specifiers” below. this list is long but we keep every single one, iykyk 💅

Asymmetric

  • rsa
  • ecc

Symmetric

  • aes
  • camellia
  • sm4

Hashing Algorithms

  • sha1
  • sha256
  • sha384
  • sha512
  • sm3_256
  • sha3_256
  • sha3_384
  • sha3_512

Keyed Hash

  • hmac
  • xor

Signing Schemes

  • rsassa
  • rsapss
  • ecdsa
  • ecdaa
  • ecschnorr
  • sm2

Asymmetric Encryption Schemes

  • oaep
  • rsaes
  • ecdh

Modes

  • ctr
  • ofb
  • cbc
  • cfb
  • ecb

Misc

  • null

🌈 Complex Specifiers

Objects, when specified for creation by the TPM, have numerous algorithms to populate in the public data. Things like type, scheme and asymmetric details, key size, etc. Below is the general format for specifying this data: <type>:<scheme>:<symmetric-details>

Type Specifiers

This portion of the complex algorithm specifier is required. The remaining scheme and symmetric details will default based on the type specified and the type of the object being created. highkey important, so read it twice if you need 💖

  • aes — default AES: aes128
  • aes128<mode> — 128 bit AES with optional mode (ctr|ofb|cbc|cfb|ecb). If mode is not specified, defaults to null.
  • aes192<mode> — same as aes128<mode>, except for a 192 bit key size.
  • aes256<mode> — same as aes128<mode>, except for a 256 bit key size.
  • sm4 — default SM4: sm4128
  • sm4128 or sm4_128 <mode> — 128 bit SM4 with optional mode (ctr|ofb|cbc|cfb|ecb). If mode is not specified, defaults to null.
  • ecc — Elliptical Curve, defaults to ecc256.
  • ecc192 or ecc_nist_p192 — 192 bit ECC NIST curve
  • ecc224 or ecc_nist_p224 — 224 bit ECC NIST curve
  • ecc256 or ecc_nist_p256 — 256 bit ECC NIST curve
  • ecc384 or ecc_nist_p384 — 384 bit ECC NIST curve
  • ecc521 or ecc_nist_p521 — 521 bit ECC NIST curve
  • ecc_sm2 or ecc_sm2_p256 — 256 bit SM2 curve
  • rsa — default RSA: rsa2048
  • rsa1024 — RSA with 1024 bit keysize.
  • rsa2048 — RSA with 2048 bit keysize.
  • rsa3072 — RSA with 3072 bit keysize.
  • rsa4096 — RSA with 4096 bit keysize.

Scheme Specifiers

Next, is an optional field, it can be skipped.

Schemes are usually Signing Schemes or Asymmetric Encryption Schemes. Most signing schemes take a hash algorithm directly following the signing scheme. If the hash algorithm is missing, it defaults to sha256. Some take no arguments, and some take multiple arguments.

Hash Optional Scheme Specifiers

These scheme specifiers are followed by a dash and a valid hash algorithm, For example: oaep-sha256.

  • oaep
  • ecdh
  • rsassa
  • rsapss
  • ecdsa
  • ecschnorr
  • sm2

Multiple Option Scheme Specifiers

This scheme specifier is followed by a count (max size UINT16) then followed by a dash(-) and a valid hash algorithm.

  • ecdaa — for example, ecdaa4-sha256. If no count is specified, it defaults to 4.

No Option Scheme Specifiers

This scheme specifier takes NO arguments.

  • rsaes — takes NO arguments, fr fr.

Symmetric Details Specifiers

This field is optional, and defaults based on the type of object being created and it’s attributes. Generally, any valid Symmetric specifier from the Type Specifiers list should work. If not specified, an asymmetric objects symmetric details defaults to aes128cfb.

Examples

Create an rsa2048 key with an rsaes asymmetric encryption scheme

tpm2_create -C parent.ctx -G rsa2048:rsaes -u key.pub -r key.priv

Create an ecc256 key with an ecdaa signing scheme with a count of 4 and sha384 hash

/tpm2_create -C parent.ctx -G ecc256:ecdaa4-sha384 -u key.pub -r
       key.priv cryptographic algorithms ALGORITHM.

⭐ COMMON OPTIONS

This collection of options are common to many programs and provide information that many users may expect. bestie, these are the ride-or-die options that show up all over the place 🫶

  • -h, --help=[man|no-man] — display the tool's manpage. By default, it attempts to invoke the manpager for the tool, however, on failure will output a short tool summary. This is the same behavior if the “man” option argument is specified, however if explicit “man” is requested, the tool will provide errors from man on stderr. If the “no-man” option if specified, or the manpager fails, the short options will be output to stdout. To successfully use the manpages feature requires the manpages to be installed or on MANPATH, see man(1) for more details.
  • -v, --version — display version information for this tool, supported tctis and exit.
  • -V, --verbose — increase the information that the tool prints to the console during its execution. When using this option the file and line number are printed.
  • -Q, --quiet — silence normal tool output to stdout.
  • -Z, --enable-errata — enable the application of errata fixups. Useful if an errata fixup needs to be applied to commands sent to the TPM. Defining the environment TPM2TOOLS_ENABLE_ERRATA is equivalent.
  • -z, --pwd-session — use password session instead of a HMAC session for authentication. A clear text password is passed to the TPM to authorize the action. This option can be used to avoid problems when unsalted sessions are used in OpenSSL FIPS mode. If auth values are used a salted session should be used for authentication.
  • -R, --autoflush — enable autoflush for transient objects created by the command. If a parent object is loaded from a context file also the transient parent object will be flushed. Autoflush can also be activated if the environment variable TPM2TOOLS_AUTOFLUSH is is set to yes or true. information many users may expect.

📡 TCTI Configuration

The TCTI or “Transmission Interface” is the communication mechanism with the TPM. TCTIs can be changed for communication with TPMs across different mediums.

To control the TCTI, the tools respect:

  1. The command line option -T or --tcti
  2. The environment variable: TPM2TOOLS_TCTI.

Note: The command line option always overrides the environment variable.

The current known TCTIs are:

  • tabrmd — the resource manager, called tabrmd. Note that tabrmd and abrmd as a tcti name are synonymous.
  • mssim — typically used for communicating to the TPM software simulator.
  • device — used when talking directly to a TPM device file.
  • none — do not initalize a connection with the TPM. Some tools allow for off-tpm options and thus support not using a TCTI. Tools that do not support it will error when attempted to be used without a TCTI connection. Does not support ANY options and MUST BE presented as the exact text of “none”.

The arguments to either the command line option or the environment variable are in the form:

<tcti-name>:<tcti-option-config>

Specifying an empty string for either the <tcti-name> or <tcti-option-config> results in the default being used for that portion respectively.

🌟 TCTI Defaults

When a TCTI is not specified, the default TCTI is searched for using dlopen(3) semantics. The tools will search for tabrmd, device and mssim TCTIs IN THAT ORDER and USE THE FIRST ONE FOUND. You can query what TCTI will be chosen as the default by using the -v option to print the version information. The “default-tcti” key-value pair will indicate which of the aforementioned TCTIs is the default. vibe check: first one found wins, no cap 💅

💜 Custom TCTIs

Any TCTI that implements the dynamic TCTI interface can be loaded. The tools internally use dlopen(3), and the raw tcti-name value is used for the lookup. Thus, this could be a path to the shared library, or a library name as understood by dlopen(3) semantics.

🌈 TCTI OPTIONS 🌈

Okay bestie, this whole little collection of options is how you tell your tool which TCTI module to talk to. There are a few known ones and they all get configured differently, so buckle up 🎀

  • device — For the device TCTI you get to pick the TPM character device file it should use. The default is /dev/tpm0.

Example: -T device:/dev/tpm0 or export TPM2TOOLS_TCTI=“device:/dev/tpm0”

  • mssim — For the mssim TCTI you can specify the domain name or IP address and the port number the simulator uses. The defaults are 127.0.0.1 and 2321.

Example: -T mssim:host=localhost,port=2321 or export TPM2TOOLS_TCTI=“mssim:host=localhost,port=2321”

  • abrmd — For the abrmd TCTI, the config string is literally just a series of simple key/value pairs, separated by a , character. Each key and each value string is separated by an = character. So chill, it's giving "very simple" energy ✨
    • The TCTI abrmd supports two keys, and here they are, no cap:
      1. bus_name : the name of the tabrmd service on the bus (a string).
      2. bus_type : the type of the dbus instance (a string), limited to session and system.

Wanna specify the tabrmd tcti name plus a config string of bus_name=com.example.FooBar? Do exactly this:

--tcti=tabrmd:bus_name=com.example.FooBar

Wanna specify the default (abrmd) tcti plus a config string of bus_type=session? Then this is your moment:

--tcti:bus_type=session
NOTE: abrmd and tabrmd are synonymous. (Also the original note just sort of trails off with "the various known TCTI modules." at the end there — I'm not gonna lie to you bestie, that fragment is exactly what it says, and I am simply reporting the tea 💀)

✨ EXAMPLES ✨

Okay so here's the little pipeline of commands, and yes these are exactly it, character for character 🫶

tpm2_createprimary -C o -c prim.ctx -Q

tpm2_create -C prim.ctx -c key.ctx -u key.pub -r key.priv -G ecc256:ecdaa

tpm2_commit -c key.ctx -t count.er \
--eccpoint-K K.bin --eccpoint-L L.bin -u E.bin

Look at that last one — that's literally the whole point of this man page, the main character herself 👑🔥

🌸 Returns 🌸

Tools can return any of the following codes, and honestly? Memorize these, they're your love language:

  • 0 — Success. Slay 💅
  • 1 — General non-specific error.
  • 2 — Options handling error.
  • 3 — Authentication error.
  • 4 — TCTI related error.
  • 5 — Non supported scheme. Applicable to tpm2_testparams.

🦋 BUGS 🦋

Github Issues. That's it, that's the section — go file 'em there, bestie 🐛

🧚 HELP 🧚

See the Mailing List. The girlies on the list will help you out 💜

⭐ License ⭐

This work is licensed under the Creative Commons Attribution 4.0 International License (CC BY 4.0). Respect the license, it's the bare minimum 🎀

And that's the whole page, bestie — tpm2-tools gave us this one, it's the tpm2_commit(1) page, and it's dated and versioned right there in the footer (source/version and date, iykyk). Go commit some keys, go be iconic, and remember: TCTI config is your friend 🌈💖

📦 where this page comes from